The disclosure relates to a piston unit and to a hydrostatic radial-piston machine having such a piston unit.
DE 40 37 455 C1, for example, discloses a hydrostatic radial-piston machine of generic type. This radial-piston machine comprises a rotor designed as a cylinder block, in which multiple piston units are displaceably guided in a radial direction. Each of these piston units has a piston, which is guided in a cylinder bore of the cylinder block and the end portion of which projecting from the cylinder block in a radial direction is supported via a rolling element on a cam plate, fixedly accommodated in a housing of the hydrostatic radial-piston machine, so that the pistons perform a lift corresponding to a lifting cam of this cam plate. One disadvantage of such piston units is that friction occurs between the piston and the rolling element interacting with this, which reduces the efficiency of a hydrostatic radial-piston machine and in particular its starting efficiency.
Various technical solutions have already been proposed to counter this disadvantage. DE 39 26 185 C2, for example, proposes that a bearing shell composed of a composite material be arranged in a roller seating compartment of a piston. The bearing composite material used for this purpose may be composed, for example, of a steel substrate with a bronze layer and a plastic layer supporting the roller. Although comparatively good friction characteristics can thereby be obtained between the seated roller and the roller seating compartment, an even greater reduction in the friction is desirable. Moreover, the production and (pre-) assembly of the bearing composite material as bearing shell prove to be relatively costly.
DE 10 2013 206 192 A1 proposes another technical solution for reducing the friction of a radial-piston machine. Here it is proposed to polish at least one surface of a piston. For this purpose, it is proposed to produce the rolling element seat from a bearing material which comprises a plastic and/or metal composite material. Although these measures achieve a comparatively high starting efficiency by reducing friction, there is still a desire for an optimal solution in terms of friction which also ensures relative ease of manufacture and assembly.
In contrast to this, the object of the disclosure is to create a piston unit and a hydrostatic radial-piston machine constructed with such a piston unit, in which the starting efficiency is improved by using the simplest possible design and/or technical production means.